In the pharmaceutical, transplant and food industries, insulated containers in combination with temperature-control agents, such as refrigerant materials, are widely used as a cost-effective system to maintain the temperature of shipped products at selected temperature ranges, including refrigeration (2-8° C.); room temperature (20-30° C.); or frozen (below 0° C.). The temperature-control agents are generally phase change materials, ice, gel packs, or dry ice.
Phase change materials are defined herein as materials which may be repeatedly converted between solid and liquid phases and utilize their latent heats of fusion to absorb, store and release energy to heat or cool during such phase conversions. In contrast to a material that absorbs and releases energy essentially uniformly over a broad temperature range, a phase change material absorbs and releases a large quantity in the vicinity of its melting/freezing point, thus facilitating temperature maintenance near the melting/freezing point.
Passive refrigerant systems utilizing insulated containers and phase change materials (and/or ice, gel packs, or dry ice) provide sufficient refrigeration for relatively short shipping periods, where, as an additional condition, the ambient temperature does not vary greatly from the internal temperature for extended periods. As shipment times are often longer than the period where ice in an insulated container will melt completely, refrigerant systems using combinations of phase change materials, gel packs and insulated containers are commonplace for shipment of temperature-sensitive products. See, e.g., U.S. Pat. Nos. 7,849,708 and 7,294,374 (both incorporated by reference). Other systems of insulated containers, and phase change materials can be used to extend the time that products within are maintained at room temperatures or at temperatures below freezing (and the latter systems may also include ice or gel packs or dry ice, as appropriate), so as to match the shipment period and the shipment conditions (most importantly, the ambient temperature).
When a number of combinations of insulated containers, phase change materials and gel packs or other materials are possible, a combination selected must be matched to expected shipment time and predicted ambient temperature, preferably with a view to selecting the lowest-cost combination for a system which can maintain the temperature required for the product.